Charged particle beam apparatuses are used in a plurality of industrial fields. Testing of semiconductor devices during manufacturing, exposure systems for lithography, detecting devices and inspection systems are only some of these fields.
In general, there is a high demand for structuring and inspecting specimens within the micrometer or nanometer scale. On such a small scale, process control, inspection or structuring is often done with charged particle beams, e.g. electron beams, which are generated and focused in charged particle beam devices, such as electron microscopes, electron beam pattern generators or charged particle inspection systems. Charged particle beams offer superior spatial resolution compared to, e.g. photon beams due to their short wavelengths.
However, for a given beam diameter, the charged particle beam current limits the throughput of charged particle beam systems. Since further miniaturization of, e.g. structures to be imaged is necessary, the charged particle beam diameter has to be decreased. As a result, the beam current for individual beams and thus, the throughput has to be decreased.
In order to increase the total charged particle beam current and thus, the throughput, a plurality of charged particle beams can be used. One option for a system applying a plurality of charged particle beams is to combine several single beam columns with each other. However, some of the components, especially magnetic lenses, cannot be miniaturized sufficiently, since the magnetic field cannot be arbitrarily increased. Thus, the columns have to be spaced such that the electron beams have a distance of 100 mm to 200 mm.
To overcome this problem, U.S. Pat. No. 3,715,580 utilizes a magnetic lens with a circular excitation coil providing two holes, each for one electron beam. Thereby, the continuous rotation symmetry of previous lenses is abandoned since the hole (optical axis) for each electron beam has different distances from the position of the excitation.
Patent application U.S. 2001/0028038A1 shows an excitation coil common to a plurality of holes in a pole piece. To increase the number of electron beams that can be used, U.S. 2001/0028038A1 uses a two-dimensional array. To compensate for the differences with respect to the focusing properties of individual beams, this prior art teaches to use lens intensity adjusters.
Since there is a strong requirement for improving resolution, for simplifying manufacturing and for minimizing aberrations in such systems, it is an object of the present invention to further improve state of the art devices.